You do the same as you do when you lose your SSH key. Restore from backup and move on with your life.
Why is there so much misinformation nonsense around passkeys?
How? Where are they stored? Which password protects them? How do I back them up? How do you move them to another device? Can I print them out on paper as a last resort measure?
Nobody fucking knows.
How do you use a restored passkey from backup? Aren't they locked to the device?